This invention relates to current limiting devices for use in electrical networks in general and more particularly to an improved current limiting device utilizing a superconductor coupled to the network.
The use of superconductors as current-limiting devices in electrical networks is known. Such use of a superconductor depends upon its property of switching over from a superconducting state into a normally conducting state when subjected to a magnetic field above that which it can tolerate and remain superconducting. One type of device is disclosed in U.S. Pat. No. 3,691,491. In this known device, the superconductor is coupled directly into the network to be protected and is designed so that at a desired overcurrent a magnetic field will exist which will cause the superconductor to go into a normally conducting state. This occurs due to the superconductor's own magnetic field. Although such devices operate quite well, they have a serious disadvantage in that each device must be designed for a particular current. Thus, for each different application a separate superconductor must be designed. It is impossible to make a single superconductor adjustable so that it can trip at any one of a plurality of desireable currents.
In view of this, the need for an improved device of this nature which permits adjusting of the tripping of the superconductor into a normally conducting state at any desired current becomes evident.